So after doing the timing belt and water pump in the legacy today, my alternator and my radiator decided to give out. I replace the alternator but I have some questions about the radiator. I have a 5eat so I have a tranny cooler built into the radiator as you know. My question is this, I can get a good deal on an aluminum MT rad for the 05-06 lgt 08-11 wrx. Would it be okay to run that radiator with an external transmission cooler. Are the fans the same between the models?

1-800 radiator got me mine same day for 120.00, fitment was great.
Do yourself a favor and watch when you disconnect the stock trans cooler lines. after not moving for 95k then bending them out of the way, after i put it all back together I had the return line split on me. Easy fix but just keep an eye out, dont want to waste all the fresh fluid you put in.

I picked up a Koyo on amazon for $120 overnight. OEM quality if not better. I had it in the car within 20min of Fedex dropping it off. I didn't have any trouble with the trans lines (at least not yet lol). Looking back now, I wish I would have had more time to wait on a Mishimoto.

FYI, I put a trans cooler only on my family beater(2001 Outback Lim) I did this because the radiator nipple for the trans cooler broke off flush(temp fix) as I was waiting on the new radiator to arrive, I noticed the car going in and out of 4th/OD, the trans would not stop doing this unless the fluid got hot, radiator replaced, no more issues. As Max Cap said, in conjunction with the stock cooler, not stand alone.

What? Your way wrong man. People run external coolers for transmissions, engines and diffs and they work great. Actually a external trans cooler, installed in a place it will get sufficient air, will have a far better cooling efficiency then the cooler located inside a radiator. Think about it, a cooler inside a radiator is being cooled by hot engine coolant where a external cooler is being cooled by air and also the time it takes the fluid to flow through the entire cooler.
If you ever worked on a EVO 10 you would notice that they have external coolers for their transmissions (auto and Mtm) transfer case and rear diffs from the factory. I have a simular set up on my Supra. One for the engine oil, my MTM and my rear diff. Granted the trans and rear diff needed a pump to circulate the fluid but it will help keep my cars drivetrain a lot cooler during events.

FYI, I put a trans cooler only on my family beater(2001 Outback Lim) I did this because the radiator nipple for the trans cooler broke off flush(temp fix) as I was waiting on the new radiator to arrive, I noticed the car going in and out of 4th/OD, the trans would not stop doing this unless the fluid got hot, radiator replaced, no more issues. As Max Cap said, in conjunction with the stock cooler, not stand alone.

Mac

Question, did you account for the extra volume the cooler requires? If you didn't then there was your problem.